1. Field of the Invention
The present invention relates to a compact and thin flat-plate antenna that is formed with a conductive flat plate, and readily housed in an electric apparatus such as a portable terminal or an electric appliance or in a wall or the like.
2. Prior Art
In recent years, various kinds of antennas dedicated to portable telephones or mobile computers (hereinafter, abbreviated as portable terminal in general) have become more and more compact except large-scale antennas for use at base stations or in satellite broadcasting. The antenna dedicated to the portable terminal is requested to be especially compact. Along with the tendency of the portable terminal toward a compact design, the antenna dedicated to the portable terminal is demanded to clear the problem of an installed space and to satisfy the demand for high performance despite limitations to the volume of the antenna. Moreover, when a wireless network is constructed at home as discussed in earnest recently, an antenna is required housed in the wall of a room or in a personal computer or any other electric appliance (hereinafter, abbreviated as electric appliance in general). In this case, the antenna has to clear the problem of its size.
The above problems are attributable to the fact that when it is intended to encase a dedicated antenna in the housing or casing (hereinafter, abbreviated as housing in general) of a portable terminal or an electric appliance, a dedicated space must be preserved inside the housing. Furthermore, when the electric appliance must be compact and lightweight, the antenna itself must also be less bulky and lightweight. In addition, the antenna must meet a demand for high performance. In other words, when an antenna offering high performance is placed in a housing, an installation space must be preserved inside the housing. Consequently, the specifications for the antenna having used heretofore must be modified. This leads to an increase in the cost of manufacturing and an extension of a development period. Therefore, for avoiding this problem, inmost cases, an external antenna is employed which is mounted using a separate housing or the like outside the housing through another cable or the like. However, in this method, when the portable terminal or electric appliance is moved, the external antenna must be often dismounted. Thereafter, the dismounted antenna must be remounted and readjusted. This is labor-intensive and time-consuming. At worst, the antenna may fail while the cable or the like are led to and fro or because of an unexpected trouble. Besides, the installed position of the portable terminal or electric appliance cannot be selected freely. This is discouraging to a user.
Consequently, a dedicated antenna housed in a portable terminal or each of home electric appliances that are interconnected over a wireless network at home is required to be easily adopted without concern about an increase in the cost of manufacturing and an extension of a development period. The antenna is also required to alleviate the user""s labor. Furthermore, the antenna itself must be low-cost.
An object of the present invention is to provide a flat-plate antenna and an electric apparatus having the flat-plate antenna. The low-cost and high-performance flat-plate antenna can be placed in a limited space inside a portable terminal or an electric appliance or housed in a wall.
In order to solve the above problems, according to one aspect of the present invention, there is provided a flat-plate antenna having a slit, which has a specified width and a specified length, formed in a conductive flat plate. Horizontal portions of the conductive flat plate separated from each other with the slit between them serve as a radiating element portion and a ground portion respectively.
According to another aspect of the present invention, it is preferred that a separate radiating portion is electrically formed in a direction different from the length direction of the radiating element portion. The radiating portion includes as an integral part thereof a conductive portion that links the radiating element portion and ground portion. Power is radiated from the radiating element portion and radiating portion.
According to still another aspect of the present invention, the length of the radiating element portion and the length of the conductive flat plate are determined so that the flat-plate antenna will exhibit predetermined excitation and predetermined directivity.
According to still another aspect of the present invention, it is preferred that the length of the radiating element portion is differentiated from the width of the ground portion so that the flat-plate antenna will exhibit predetermined excitation and predetermined directivity.
According to still another aspect of the present invention, it is preferred that the length of the radiating element portion is substantially a multiple of a quarter of a wavelength attained at the operating frequency of the antenna by an odd-numbered value.
What is referred to as the operating frequency is an operating frequency at which the flat-plate antenna according to the present invention operates when housed in a certain housing and which depends on the position of the flat-plate antenna inside the housing. If the flat-plate antenna according to the present invention is housed in a wall or the like, the operating frequency depends on how the flat-plate antenna is housed.
The slitted shape of the flat-plate antenna may be varied depending on a power supply structure to be described later. Namely, the radiating element portion and ground portion may neither be parallel to each other nor be separated from each other by an even distance.
According to still another aspect of the present invention, a conductive line may be extended from part of the radiating element portion. The conductive line formed as an integral part of the radiating element portion may be used as part of a power line over which power is supplied to the antenna.
According to still another aspect of the present invention, a conductive line may be extended from part of the ground portion. The conductive line formed as an integral part of the ground portion may be used as part of a power line over which power is supplied to the antenna.
According to still another aspect of the present invention, a conductive plane formed on an insulating base may be adopted as the conductive flat plate.
The conductive plane is machined according to a method of plating the base or any other method.
According to still another aspect of the present invention, the conductive flat plate may have the shape thereof varied depending on the shape or situation of an installed position of the flat-plate antenna. For example, the conductive flat plate may have a three-dimensional shape, or may have part or the whole thereof streamlined.
According to still another aspect of the present invention, a power line over which power is supplied to the antenna may be brought into contact with the radiating element portion and the ground portion, and thus electrically coupled to the radiating element portion and the ground portion.
According to still another aspect of the present invention, a wiring pattern drawn on a substrate may be adopted as a power line over which power is supplied to the antenna. The power line may be electrically coupled to the radiating element portion and ground portion respectively.
A coaxial line composed of an inner conductor and an outer conductor may be adopted as a power line over which power is supplied to the antenna. The inner conductor is formed with a strand that includes a single wire or a plurality of wires. The outer conductor is mounted on the periphery of the inner conductor. The inner conductor and outer conductor bared at one end of the coaxial line may be coupled to the radiating element portion and ground portion respectively.
For connecting part of the radiating element portion to part of the ground portion using the inner conductor and outer conductor constituting the coaxial line, not only fusion using a conductive soldering material but also connection using connectors or the like may be adopted according to a purpose of use.
Preferably, a position on the radiating element portion at which the radiating element portion is coupled to the power line is determined in order to attain an impedance match. Moreover, a position on the ground portion at which the ground portion is coupled to the power line is determined in order to attain an impedance match.
Preferably, the above-described flat-plate antenna is placed inside an electric apparatus.
According to still another aspect of the present invention, a low-cost flat-plate antenna is so compact and thin that it can be placed in a space, which is as limited as a gap, inside a housing of a portable terminal or the like. The flat-plate antenna operates without exhibiting directivity with respect to the horizontal plane of the portable terminal or the like.
According to still another aspect of the present invention, when a separate antenna is located near the flat-plate antenna, the directivity of the antenna can be controlled while differentiated between the flat-plate antenna opposed to the separate antenna and the opposite portion thereof. Therefore, the electromagnetic interference will not occur. Moreover, a distance from the flat-plate antenna to the separate antenna can be reduced without impairment of the properties of the antenna.